The aforementioned devices generally include a pulse generator which is able to monitor the patient's cardiac activity and to generate shock pulses of high energy when the heart presents a ventricular arrhythmia that is deemed suitable to be treated. When the pulse energy lies between 0.1 and approximately 10.0 Joules (J), this therapy is called “cardioversion” and the electric shock delivered is called “cardioversion shock.” When the energy is higher than approximately 10.0 J, the therapy is called defibrillation and the electric shock is then called a “defibrillation shock.”
Such devices are known in the art, as described, for example, in EP-A-0 626 182 and its corresponding U.S. Pat. No. 5,462,060, and EP-A-0 838 235 and its corresponding U.S. Pat. No. 5,868,793 (all commonly assigned to the assignee hereof Ela Medical S.A., Montrouge, France).
A tachyarrhythmia condition as used in this art and herein actually encompasses several different possible cardiac activity situations. These include ventricular fibrillation (VF), ventricular tachycardia (VT), sinusal tachycardia (ST), and supraventricular tachycardia (SVT, which is a tachycardia of atrial origin).
As soon as a disorder of the ventricular rhythm is recognized by the pulse generator and proven (i.e., is determined to be either ventricular tachycardia or ventricular fibrillation in the known manner), as known in the art, the currently available defibrillators generally apply a differentiated therapy, as follows. In the event of an organized ventricular tachycardia, there is first an application of an ATP therapy mode, which is then followed by application of a shock (cardioversion or defibrillation, as may be appropriate) if the ATP stimulation is ineffective. In the event of ventricular fibrillation, the therapy mode is an immediate application of a shock (again cardioversion or defibrillation, as appropriate in the case), which is the only appropriate therapy because the life of the patient is then deemed to be at risk.
In the first case (organized VT), except for some syncope episodes, the urgency of delivering a shock therapy mode is less than in the case of a VF, especially when the tachycardia is of a relatively low frequency. Certain clinical studies have suggested, however, that these two populations, one treated initially with ATP, the other immediately treated by a shock, present in fact during follow-up study an approximately identical number of delivered shocks. This would seem to suggest that the ATP therapy mode, even if it is effective, nevertheless does not prevent the occurrence of a more serious event requiring a treatment by a shock therapy mode.
One disadvantage of an immediate treatment with a shock is the pain felt by the patient, and the situation of discomfort in daily life in living in fear of a future shock.
It also has been suggested by certain studies that many VT conditions could terminate spontaneously, if it were possible to wait. Unfortunately, however, it is generally necessary to treat the patient quickly because these VT conditions are not well supported by the patent.
It is therefore desirable to provide a device that, in the event of an organized ventricular tachycardia, can apply at least temporarily a therapy mode other than a shock therapy, but which mode would be more effective than the known ATP stimulation therapy.